Rotary cutting machines generally include a frame which supports one or more horizontally rotatable cutter blades, a shroud for covering the blades and directing the flow of cut material, and means for rotating the blades to achieve a cutting action. Small rotary cutting machines such as riding lawn mowers and the like generally have belt driven cutting blades. Some large grass cutting machines designed to be towed behind a tractor vehicle are driven directly from a power take-off shaft. For heavy duty rotary cutting machines intended for cutting coarse weeds, brush and small trees, however, an independent power source for each cutter is generally required to generate the torque for maintaining a high speed of rotation while cutting coarse material. Heavy duty rotary cutting machines are therefore commonly equipped with a hydraulic motor or the like for driving each cutting blade. If the cutting blade of such a machine strikes an object possessing considerable inertia, a tremendous amount of torque is generated, inducing significant stress in the points of connection between the motor and the frame of the machine. Such torque may be sufficient to damage the motor and/or shear its connection with the frame. To prevent such damage, cotter pins or torque reducing slip couplings have been used to connect the driving shaft to the cutting blade. However, it is a disadvantage of such a construction that the connection between the motor and the cutter frame is still subjected to torque shocks each time the rotating cutting blade strikes an object possessing sufficient inertia to induce rotation of the motor with respect to the frame. Repeated torque shocks may contribute to fatigue of the connection and ultimately to damage of the machine. Furthermore, the operation of the rotary cutting machine must be stopped each time a broken cotter pin requires replacement.
Thus, there is a recognized need for a motor mount capable of absorbing the torque shock created when a rotating cutting blade strikes an object possessing considerable inertia, in order to prevent damage to the motor, the shaft or the cutter frame and to permit continuous operation of the rotary cutter.
Shock absorbing motor mounts for hydraulic motors are known. A shock absorbing motor mount for a hydraulic motor used in a tumbler-type finishing machine is taught in U.S. Pat. No. 4,232,486 issued to John F. Rampe. The tumbler machine includes a drum which is rotatably mounted to a supporting framework by a drive shaft journaled through a thrust bearing. A hydraulic motor is rigidly affixed to a free end of the drive shaft. A rotation of the motor housing with respect to the supporting framework is prevented by a number of shock absorbing torsion rods which extend tangentially from the housing and connect the motor with the supporting framework. Each of the rods is pivotally connected to the motor on their one end, while the other end extends through a bore in the supporting framework. The other end of each rod is resiliently connected to the supporting framework by opposed helical springs. The springs are coaxial with the rod and are positioned on each side of the framework. They are tensioned between the supporting framework and appropriate spring retainers mounted on the rod. The housing of the motor is not directly attached to the supporting frame structure. This shock absorbing arrangement may work well for a slowly rotating tumbler-type machine, because the shock absorber is only employed for minimizing the transmission of transient loads and shocks from the drum to the supporting framework, since extreme torque shocks are not commonly generated in such tumbler machines. However, if used on a heavy duty cutter rotating at high speed, a shock absorbing motor mount as described by Rampe could cause excessive vibration of the motor that could result in damage to the shaft, especially if the rotating blade were to strike an object possessing significant inertia.